The line (rather than continuous) emission spectrum of hydrogen provides evidence that electrons occupy:
A continuous range of energies
Discrete energy levels
The nucleus
Random positions
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WhyA line spectrum shows only certain discrete frequencies, which is evidence that electrons exist in discrete (quantised) energy levels rather than a continuous range of energies.
2Multiple choice · Easy
What is the full ground-state electron configuration of a sodium atom (Z = 11)?
$1s^{2}\,2s^{2}\,2p^{6}\,3s^{1}$
$1s^{2}\,2s^{2}\,2p^{6}$
$1s^{2}\,2s^{2}\,2p^{5}\,3s^{2}$
$1s^{2}\,2s^{2}\,2p^{6}\,3s^{2}$
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WhyFilling in order of increasing energy: $1s^{2}\,2s^{2}\,2p^{6}\,3s^{1}$ accounts for all 11 electrons.
3Multiple choice · Medium
What is the maximum number of electrons that a $p$ sublevel can hold?
2
6
8
10
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WhyA $p$ sublevel contains 3 orbitals, and each orbital holds a maximum of 2 electrons, giving $3 \times 2 = 6$ electrons.
4Multiple choice · Medium
What is the ground-state electron configuration of a chlorine atom (Z = 17)?
$1s^{2}\,2s^{2}\,2p^{6}\,3s^{2}\,3p^{5}$
$1s^{2}\,2s^{2}\,2p^{6}\,3s^{2}\,3p^{6}$
$1s^{2}\,2s^{2}\,2p^{6}\,3s^{2}\,3d^{5}$
$1s^{2}\,2s^{2}\,2p^{5}\,3s^{2}\,3p^{6}$
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WhySeventeen electrons fill as $1s^{2}\,2s^{2}\,2p^{6}\,3s^{2}\,3p^{5}$.
5Multiple choice · Medium
As the energy (frequency) increases, the lines in the emission spectrum of hydrogen:
Get further apart
Converge (get closer together)
Stay equally spaced
Disappear entirely
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WhyThe energy levels converge at higher energy, so the spectral lines get closer together (converge) towards the high-frequency end, eventually reaching a convergence limit.
6Multiple choice · Hard
How many orbitals are there in the third main energy level (n = 3)?
3
6
9
18
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WhyFor $n=3$ there are sublevels $3s$ (1 orbital), $3p$ (3 orbitals) and $3d$ (5 orbitals), giving $1 + 3 + 5 = 9$ orbitals ($n^{2}$).
7Fill in the blank · Easy
The ground-state electron configuration of oxygen (Z = 8) ends in $2p^{}$.
Answer:
4 / four
WhyOxygen has 8 electrons: $1s^{2}\,2s^{2}\,2p^{4}$, so the configuration ends in $2p^{4}$.
8Fill in the blank · Medium
An orbital that has a spherical shape is an orbital.
Answer:
s / s orbital
Why$s$ orbitals are spherically symmetrical around the nucleus, whereas $p$ orbitals are dumb-bell (lobed) shaped.
9Multiple choice · Medium
Which pair of species has the same number of outer-shell electrons?
Mg2+ and F-
Na+ and Mg2+
Cl- and Ca2+
O2- and Al3+
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WhyAn ion such as Mg2+ loses its valence shell to reach a noble-gas configuration, while F- gains one electron to do the same, so both finish with eight outer electrons.
10Multiple choice · Hard
Species P2+ has 10 electrons and species Q- has 10 electrons. What can be concluded about their outer shells?
Both have eight outer electrons and identical electron configurations
They have different numbers of outer electrons
P2+ has more outer electrons than Q-
Neither obeys the octet rule
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WhyBoth species have 10 electrons arranged as 1s2 2s2 2p6, so each has a complete octet of eight outer electrons; they are isoelectronic.
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